1. Field of the Invention
The present invention relates to photoactive electronic devices in which there is at least one active layer comprising an electron transport and/or anti-quenching composition.
2. Description of the Related Art
In organic photoactive electronic devices, such as light-emitting diodes (“OLED”), that make up OLED displays, the organic active layer is sandwiched between two electrical contact layers in an OLED display. In an OLED the organic photoactive layer emits light through the light-transmitting electrical contact layer upon application of a voltage across the electrical contact layers.
It is well known to use organic electroluminescent compounds as the active component in light-emitting diodes. Simple organic molecules, conjugated polymers, and organometallic complexes have been used.
Devices which use photoactive materials, frequently include one or more charge transport layers, which are positioned between the photoactive (e.g., light-emitting) layer and one of the contact layers. A hole transport layer may be positioned between the photoactive layer and the hole-injecting contact layer, also called the anode. An electron transport layer may be positioned between the photoactive layer and the electron-injecting contact layer, also called the cathode.
When organometallic compounds, such as Ir and Pt complexes, are used as the electroluminescent layer, a blocking layer inserted next to the luminescent layer on the cathode side can enhance the device efficiency. 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (known as BCP or DDPA) was used by Baldo et al. for this purpose. It was proposed that the BCP layer functions as an “exciton blocker” to prevent the transfer of the energy of a luminescent exciton to the adjacent layer. The blocking layer is characterized by a band gap greater than the energy level of excitons formed in the luminescent layer.
U.S. Pat. No. 6,097,147 claims a light emitting device comprising: a substantially transparent anode; a hole transporting layer over said anode; an emission layer over said hole transporting layer; a blocking layer over said emission layer; an electron transporting layer over said blocking layer; and a cathode in electrical contact with said electron transporting layer. It further claims a device wherein said blocking layer is characterized by a band gap greater than the energy level of excitons formed in said emission layer.
However, energy transfer from photoactive materials to an adjacent layer can be quenched not only by energy transfer but also by electron transfer to the adjacent layer, so the use of larger band gap exciton blocker is insufficient. Materials that can prevent both energy transfer quenching and electron transfer quenching are needed.